Q&A: Switching from 3-Wire to 4-Wire 240-Volt Appliance

A. You’re probably better off calling an electrician; but if you plan to do the work yourself, first determine if the appliance is fed from a main panel or a subpanel. If the feed is from a subpanel, you must install a new four-wire circuit to the appliance to comply with code. Bonding the neutral (grounded circuit conductor) and the ground wire anywhere but at the main panel is a big no-no. If the feed is from the main panel, you can connect the ground wire attached to the frame of the unit (green or bare) to the neutral terminal on the terminal block and change the pigtail to a three-wire type. But when possible, installing a four-wire circuit is still preferable.

Here in the Southwest, most houses are built slab-on-grade and have flat roofs. If you don’t have an attic or crawlspace, and the appliance is on or near an exterior wall, you can install new conduit on the exterior. Between the exterior wall and the appliance, there are often cabinets behind which you can hide conduit, with little intrusion or patching. Flexible conduit can be helpful here.